The field relates to thrust bearings, particularly to rolling thrust bearings. The field also relates to rolling thrust bearings for pistons used in internal combustion engines. More particularly, this field covers piston rolling thrust bearing constructions for coupling a piston to connecting linkage of an internal combustion engine.
Opposed-piston diesel engines have an acknowledged potential for superior performance according to standard measures of output power and fuel efficiency. For example, the Rootes-Lister diesel engine (also known as the Commer ‘TS3’ diesel) illustrated in FIG. 1 advanced two-stroke engine construction by way of an engine configuration which included three pairs of opposed pistons driving a single crankshaft. Each piston was coupled to a respective crankpin by a rocker assembly. Each rocker assembly included a rocker arm pivoted between two ends, a piston rod connected to a first end of the rocker arm and to a wrist pin located inside the piston, and a connecting rod connecting the second end of the rocker arm to a crankpin. All of the rocker assemblies were identical, with each rocker arm end being pivoted to the engine frame. The architecture of the rocker assemblies significantly reduced side forces acting on the pistons, thereby making the engine very durable. However, at least one construction feature severely compromised the performance of the Rootes-Lister engine.
In the Rootes-Lister engine wrist pins (“gudgeon” pins, UK) were mounted inside the pistons, which limited the size of the bearings for the pins, and therefore the ultimate load bearing capacity of the pistons. As a result of this and other constraints, the engine was limited to operating at very low power levels (about 38 HP/liter).
Examples of opposed piston engine constructions that remove wrist pins from inside pistons are found in Great Britain Patent 558,115 and in U.S. Pat. Nos. 7,156,056 B2 and 7,360,551 B2. In each case, there is no articulation of the piston-to-crankshaft linkage that is internal to the piston. Instead, joints external to the pistons couple the linear motions of the pistons to each of a pair of crankshafts located above and below the cylinders. The axes of the crankshafts lie in a plane that is normal to the axes of, and that bisects, the cylinders. Both crankshafts are connected to each pair of opposed pistons through multiple connecting rods. Consequently, very close tolerances must be maintained during manufacturing to avoid, or at least mitigate, misalignment between the connecting rods and external wrist pins that could result in undesirable side forces exerted on the pistons. A consequence of coupling both crankshafts to the single wrist pin of each piston is an over constraint condition whereby unequal elastic deformation of the coupling components can lead to significant deflection of the wrist pin in a direction orthogonal to the piston motion that produces undesirable side forces acting on the piston.
Accordingly, the potentially high power levels in two-stroke, opposed-piston engines have not been fully achieved by single crankshaft constructions with rocker assemblies because wrist pins are located inside the pistons. However, dual-crankshaft constructions in which the wrist pins have been removed from, and relocated outside of, the pistons have also not achieved full power potential due to side forces resulting from over constraint of the wrist pins.